Copper-tin electrolyte and process for the deposition of bronze layers

ABSTRACT

Consumer goods and industrial articles are electroplated with bronze layers for decorative purposes and for protection against corrosion. The electrolytes used hitherto for producing decorative bronze layers are cyanide-containing or, as in the case of baths based on organosulfonic acids, highly corrosive, or, as in the case of cyanide-free baths based on diphosphoric acid, give unsatisfactory brightness and shine. The present invention provides a nontoxic electrolyte for the electrochemical deposition of uniformly bright and shiny bronze layers and a corresponding process for the application of such decorative bronze layers to consumer goods and industrial articles, by means of which relatively thick bronze layers can also be deposited electrochemically in a satisfactory way.

The invention relates to a copper-tin electrolyte which is free of toxicconstituents such as cyanides. In particular, the invention relates to acorresponding electrolyte having a novel brightener system. It likewiseencompasses a process for the deposition of decorative, white and yellowbronze layers on consumer goods and industrial articles using theelectrolyte of the invention.

Consumer goods or consumer articles as defined in the consumer articlesregulations are finished with thin, oxidation-stable metal layers fordecorative reasons and in order to prevent corrosion. These layers haveto be mechanically stable and should not display any tarnishing or signsof wear even after prolonged use. Since 2001, the sale of consumer goodscoated with nickel-containing finishing alloys has no longer beenpermitted, or is possible only with observance of strict conditions, inEurope pursuant to EU directive 94/27/EC since nickel andnickel-containing metal layers are contact allergens. Bronze alloys inparticular have become established as a replacement fornickel-containing finishing layers and these enable such mass-producedconsumer goods to be finished inexpensively in barrel or rackelectroplating processes to give allergen-free, attractive products.

In the production of bronze layers for the electronics industry, thesolderability of the resulting layer and, if appropriate, its mechanicaladhesive strength are the critical properties of the layer to beproduced. For use in this field, the appearance of the layers isgenerally less important than their functionality. On the other hand,for production of bronze layers on consumer goods, the decorative effect(shine and brightness) and also a long service life of the resultinglayer with an essentially unchanged appearance are the important targetparameters.

Apart from the conventional processes for producing bronze layers, whichuse cyanide-containing and thus highly toxic, alkaline baths, variouselectroplating processes which can, according to the composition oftheir electrolytes, usually be assigned to one of two main groups foundin the prior art are also known: processes using electrolytes based onorganosulfonic acids or processes using baths based on diphosphoric acid(pyrophosphoric acid). For the purposes of the present text, “nontoxic”means that the electrolytes according to the invention described in thisway do not contain any materials which are classified as “toxic” (T) or“very toxic” (T⁺) according to the regulations applicable in Europe forhandling dangerous goods and hazardous materials.

For example, EP 1 111 097 A2 describes an electrolyte comprising anorganosulfonic acid and ions of tin and copper together with dispersantsand brightening additives and also, if appropriate, antioxidants. EP 1408 141 A1 describes a process for the electrochemical deposition ofbronzes, in which an acidic electrolyte comprising tin and copper ionstogether with an alkylsulfonic acid and an aromatic, nonionic wettingagent. DE 100 46 600 A1 describes an alkylsulfonic or alkanolsulfonicacid-containing bath which comprises soluble tin and copper saltstogether with organic sulfur compounds, and a process using this bath.

A significant disadvantage of such electrolytes produced on the basis oforganosulfonic acids is their high corrosivity. For example, baths basedon methanesulfonic acids frequently have pH values below one. The highcorrosivity of these baths limits their use range in respect of thesubstrate materials to be finished and requires the use of particularlycorrosion-resistant working materials for carrying out the process.

EP 1 146 148 A2 describes a cyanide-free copper-tin electrolyte based ondiphosphoric acid, which in addition to the reaction product of an amineand an epihalohydrin in a molar ratio of 1:1 contains a cationicsurfactant. WO 2004/005528 describes a cyanide-free diphosphoricacid-copper-tin electrolyte which contains an additive composed of aminederivative, an epihalohydrin and a glicidyl ether compound. Electrolytesbased on diphosphoric acid generally have very limited long-termstabilities and have to be renewed frequently.

In addition, processes for producing solderable copper-tin layers whichcan be used as replacement for tin-lead solders and in which a wideselection of acidic base electrolytes can be used are known from theelectronics industry. Thus, EP 1 001 054 A2 describes a tin-copperelectrolyte which comprises a water-soluble tin salt, a water-solublecopper salt, an inorganic or organic acid or a water-soluble saltthereof and also one or more compounds from the group consisting ofgenerally toxic thiourea or thiol derivatives. The inventive bathdescribed there can additionally contain one or more compounds selectedfrom the group consisting of carboxylic acids, lactones, phosphoric acidcondensates, phosphonic acid derivatives or water-soluble salts of theseor combinations thereof.

WO2004/005528 describes a cyanide-free diphosphoric acid-copper-tinelectrolyte which contains an additive composed of an amine derivative,an epichlorohydrin and a glycidyl ether compound in a molar ratio of1:0.5-2:0.1-5. It was an object of this document to further widen thecurrent density range in which uniform deposition of the metals in ashiny layer can be achieved. It is explicitly mentioned that suchdeposition can only be attained when the additive added is made up ofall three of the abovementioned components.

In view of the prior art just cited, it can be noted that thosedeposition processes which ensure uniform deposition on metals over awide current density range and also use electrolytes which appeareconomically and ecologically advantageous in terms of their compositionare particularly advantageous. Furthermore, a successful electrolyteshould allow uniformly bright and shiny layers to be obtained,regardless of the thickness of the bronze layer deposited.

It is therefore an object of the present invention to provide anelectrolyte which has long-term stability, is suitable for appropriatelyadvantageous deposition of mechanically stable and decorativelyadvantageous bronze layers on consumer goods and industrial articles andis free of toxic constituents. It is a further object of the presentinvention to provide a process for the application of decorative bronzelayers to consumer goods and industrial articles using such anelectrolyte.

These objects and further objects which are not mentioned at the presentjuncture but can be derived in an obvious way from the prior art areachieved by specification of an electrolyte having the features of thepresent claim 1 and its use in a deposition process according to theinvention as set forth in claim 13. Preferred embodiments referring backto these claims are defined in claims 2 to 12 and 14-15.

The provision of a nontoxic electrolyte for the deposition of decorativebronze alloy layers on consumer goods and industrial articles, whichelectrolyte contains the metals to be deposited in the form ofwater-soluble salts and further comprises one or more phosphonic acidderivatives as complexing agents and also a brighter system composed ofa disulfide compound and a carbonate or hydrogencarbonate salt,completely surprisingly but nonetheless advantageously achieves thestated objects. The inventive electrolyte having a different compositionthan in the prior art makes it possible to obtain excellent electrolyticdeposits of bronze layers. In particular, the good brightness and shineof the bronze layers can be obtained independently of their thickness.The alloy composition remains approximately constant over a wide currentdensity range, which is in no way suggested by the prior art.

In the electrolyte of the invention, the metals copper and tin orcopper, tin and zinc to be deposited are present in dissolved form astheir ions. They are preferably introduced in the form of water-solublesalts which are preferably selected from the group consisting ofpyrophosphates, carbonates, hydroxide-carbonates, hydrogencarbonates,sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides,oxide-hydroxides, oxides or combinations thereof. Very particularpreference is given to the embodiment in which the metals are used inthe form of salts with ions selected from the group consisting ofpyrophosphate, carbonate, hydroxide-carbonate, oxide-hydroxide,hydroxide and hydrogencarbonate. Which salts are introduced in whichamount into the electrolyte can determine the color of the resultingdecorative bronze layers and can be adjusted according to customerrequirements. The metals to be deposited are, as indicated, present inionically dissolved form in the electrolyte for application ofdecorative bronze layers to consumer goods and industrial articles. Theion concentration of copper can be set in the range from 0.2 to 10 g/l,preferably from 0.3 to 4 g/l, of electrolyte, the ion concentration oftin can be set in the range from 1.0 to 30 g/l, preferably 2-20 g/l, ofelectrolyte and, if present, the ion concentration of zinc can be set inthe range from 1.0 to 20 g/l, preferably 0-3 g/l, of electrolyte. Forthe finishing of consumer goods, the metals to be deposited areparticularly preferably introduced as salt of a pyrophosphate,carbonate, hydrogencarbonate or hydroxide-carbonate in such a way thatthe resulting ion concentration is in the range from 0.3 to 4 gram ofcopper, from 2 to 20 gram of tin and from 0 to 3 gram of zinc, in caseper liter of electrolyte.

The electrolyte of the invention has some concentration of carbonate orhydrogencarbonate ions. These can be present in the electrolyte in theform of preferably soluble salts selected from the group consisting ofalkali metal and alkaline earth metal salts, in particular sodium orpotassium carbonate or sodium or potassium hydrogencarbonate. However,the embodiment in which the metals which are used and are to bedeposited are also added either completely or partly in the form ofcarbonates or hydrogencarbonates to the electrolyte is preferred. Theembodiment in which only copper is present as carbonate in the bathformulation is advantageous. Tin and zinc and also, during operation ofthe bath, copper are then advantageously added as pyrophosphate.Addition of the abovementioned salts enables a concentration ofcarbonate or hydrogencarbonate ions in the electrolyte of from 0.5 to100 g/l of electrolyte to be set. The concentration is particularlypreferably in the range from 5 to 40 g/l and very particularlypreferably from 15 to 30 g/l.

As further components of the electrolyte, mention may be made ofdisulfide compounds. These can advantageously be selected from the groupconsisting of substituted and unsubstituted bisalkyl or bis(hetero)arylor alkyl (hetero)aryl disulfides, in particular those of the generalformula (I),

R—S—S—R′  (I)

wherein

R and R′ can each be, independently of one another, substituted orunsubstituted (C₁-C₈)-alkyl, (C₃-C₆)-cycloalkyl, (C₇-C₁₉)-alkylaryl,(C₆-C₁₈)-aryl, (C₇-C₁₉)-aralkyl, (C₃-C₁₈)-heteroaryl,(C₄-C₁₉)-alkylheteroaryl, (C₄-C₁₉)-heteroaralkyl. R and R′ can also bejoined to form a ring. Possible substitutents for R and R′ are inprinciple all groups of substituents which a person skilled in the artwould consider for this purpose. These are, in particular, substituentsselected from the group consisting of amine radicals, nitro groups,hydroxyl radicals, halide radicals, acid radicals such as carboxylicacids, sulfonic acids and phosphonic acids.

Particularly advantageous disulfide compounds are compounds selectedfrom the group consisting of 2,2′-dithiodipyridine,4,4′-dithiodipyridine, 6,6′-dithiodinicotinic acid, bis(4-aminophenyl)disulfide, 2,2′-dithiosalicylic acid, D-cystine, L-cystine, DL-cystine,2,2′-dithio(bis)benzothiazole, 2,2′-dithiobis(5-nitropyridine). Veryparticular preference is given in this context to the compoundbis-(3-sodium sulfopropyl) disulfide, referred to as SPS for short. Thedisulfide compounds are preferably used in an amount of from 0.01 mg perliter to 10.0 g per liter of electrolyte. Particular preference is givento use in a concentration range from 0.5 mg per liter to 7.5 g per literof electrolyte. The disulfide compound, in particular the abovementionedSPS, is very particularly preferably used in a concentration range from0.1 mg per liter to 5 g per liter in the electrolyte.

The application of the decorative bronze layers to consumer goods andindustrial articles using the electrolyte of the invention is effected,as indicated, in an electroplating process. It is important here thatthe metals to be deposited are kept permanently in solution during theprocess, regardless of whether electroplating is carried out in acontinuous process or in a batch process. To ensure this, theelectrolyte of the invention contains phosphonic acids as complexingagents.

Preference is given to using compounds selected from the groupconsisting of hydroxyphosphonic, nitrilophosphonic or aminophosphonicacid, e.g. 1-aminomethylphosphonic acid AMP,aminotris(methylenephosphonic acid) ATMP, 1-aminoethylphosphonic acidAEP, 1-aminopropylphosphonic acid APP,(1-acetylamino-2,2,2-trichloroethyl)phosphonic acid,(1-amino-1-phosphonooctyl) phosphonic acid,(1-benzoylamino-2,2,2-trichloroethyl)phosphonic acid,(1-benzoylamino-2,2-dichlorovinyl)phosphonic acid,(4-chlorophenylhydroxymethyl)phosphonic acid,diethylenetriaminepenta(methylenephosphonic acid) DTPMP,ethylenediaminetetra(methylenephosphonic acid) EDTMP,1-hydroxyethane(1,1-diphosphonic acid) HEDP,hydroxyethylamino-di(methylenephosphonic acid) HEMPA,hexamethylenediaminetetra(methylphosphonic acid) HDTMP,((hydroxymethylphosphonomethylamino)methyl)phosphonic acid,nitrilotris(methylenephosphonic acid) NTMP,2,2,2-trichloro-1-(furan-2-carbonyl)amino ethylphosphonic acid, saltsderived therefrom and condensates derived therefrom, or combinationsthereof.

Particular preference is given to using one or more compounds selectedfrom the group consisting of aminotris(methylenephosphonic acid) ATMP,diethylenetriamine-penta(methylenphosphonic acid) DTPMP,ethylenediaminetetra(methylenephosphonic acid) EDTMP,1-hydroxyethane(1,1-diphosphonic acid) HEDP,hydroxyethylamino-di(methylenephosphonic acid) HEMPA,hexamethylenediaminetetra(methylphosphonic acid) HDTMP, salts derivedtherefrom and condensates derived therefrom, or combinations thereof.Preference is given to using from 10 to 400 gram of phosphonic acidderivatives per liter of electrolyte, particularly preferably from 20 to200 gram per liter of electrolyte and very particularly preferably from50 to 150 gram per liter of electrolyte.

The pH of the electrolyte is in the range from 6 to 14 required for theelectroplating application. Preference is given to a range of 8-12 andvery particular preference to about 10.

Apart from the metals to be deposited, the phosphonic acid derivativesused as complexing agent and the brightener system composed ofhydrogencarbonate salt and disulfide compound which is used, theelectrolyte can contain further organic additives which assume functionsas complexing ligands, brighteners, wetting agents or stabilizers. Theelectrolyte of the invention can also dispense with the use of cationicsurfactants. The addition of further brighteners and wetting agents isonly preferred in the case of the appearance of the decorative bronzelayers to be deposited having to meet special requirements. They make itpossible to adjust not only the color of the bronze layers, whichdepends critically on the ratio of the metals to be deposited, but alsothe shine of the layers in all gradations from matt silk to high gloss.

Preference is given to adding one or more compounds selected from thegroup consisting of monocarboxylic and dicarboxylic acids and theirsalts, sulfonic acids and their salts, betaines and aromatic nitrocompounds. These compounds act as electrolyte bath stabilizers.Particular preference is given to using oxalic acid, alkanesulfonicacids, in particular methanesulfonic acid, or nitrobenzotriazoles ormixtures thereof. Suitable alkanesulfonic acids are disclosed, forexample, in EP1001054.

As sulfonic acids, it can also be advantageous to use those of thegeneral formula (II) or salts thereof.

R—SO₃H  (II)

where

R is substituted or unsubstituted (C₁-C₈)-alkyl, (C₃-C₆)-cycloalkyl,(C₇-C₁₉)-alkylaryl, (C₆-C₁₈)-aryl, (C₇-C₁₉)-aralkyl,(C₃-C₁₈)-heteroaryl, (C₄-C₁₉)-alkylheteroaryl, (C₄-C₁₉)-heteroaralkyl.Possible substituents for R and R′ are in principle all groups ofsubstituents which a person skilled in the art would consider for thispurpose. These are, in particular, substituents selected from the groupconsisting of amine radicals, nitro groups, hydroxyl radicals, halideradicals, acid radicals such as carboxylic acids, sulfonic acids andphosphonic acids. This applies analogously to the corresponding salts,in particular salts with cations of the alkali metals or alkaline earthmetals.

Preferred compounds are those selected from the group consisting of3-mercapto-1-propanesulfonic acid Na salt,3-(2-benzothiazolyl-2-mercapto)propanesulfonic acid Na salt,saccharin-N-propylsulfonate Na salt, 3-sulfopropyl N,N-dimethyldithiocarbamate Na salt, 1-propanesulfonic acid and3[(ethoxythioxomethyl)thio] K salt.

In this context, very particular preference is given to the disulfiderequired for the brightener system and the sulfonic acid being presentin one compound, as is the case, for example, for bis-(3-sodiumsulfopropyl) disulfide.

It is also possible to use, for example, citric acid as carboxylic acid(Jordan, Manfred, Die galvanische Abscheidung von Zinn undZinnlegierungen, Saulgau 1993, page 156). Betaines to be used canpreferably be found in WO2004/005528 or in Jordan, Manfred (Diegalvanische Abscheidung von Zinn und Zinnlegierungen, Saulgau 1993, page156). Particular preference is given to those presented in EP636713.Further additives may be found in the literature (Jordan, Manfred, Diegalvanische Abscheidung von Zinn und Zinnlegierungen, Saulgau 1993).

Further complexing ligands which can advantageously be used arepyrophosphate ions. These can be present in the electrolyte and canadvantageously be introduced into the electrolyte as anions of the metalsalts to be deposited. However, the embodiment in which thepyrophosphate ions are added in the form of salts of other metals, inparticular of alkali and alkaline earth metals in the electrolyte, islikewise possible. The amount of pyrophosphate ions can be set in aprecise manner by a person skilled in the art. It is limited by the factthat the concentration in the electrolyte should be above a minimumamount in order to be able still to bring about the effect discussed toa sufficient extent. On the other hand, the amount of pyrophosphate tobe used is guided by economic aspects. In this context, reference may bemade to EP1146148 and the relevant information presented there. Theamount of pyrophosphate to be used in the electrolyte is preferably1-400 g/l. Particular preference is given to using an amount of 2-200g/l of electrolyte. The pyrophosphate can, if it is, as indicated, notintroduced as salt constituent of the metals to be deposited, be used assodium or potassium diphosphate or as H₂P₂O₇ in combination with a baseof the alkali or alkaline earth metals. Preference is given to usingK₂P₂O₇ for this purpose.

The electrolyte of the invention is free of hazardous materialsclassified as toxic (T) or very toxic (T⁺). No cyanides, no thioureaderivatives or similarly toxic materials are present. The nontoxicelectrolyte of the invention is particularly suitable for theelectrochemical application of decorative bronze layers to consumergoods and industrial articles. It can be used in barrel, rack, belt orreel to reel electroplating plants.

In a corresponding process for the electrochemical application ofdecorative bronze alloy layers, the consumer goods and industrialarticles to be coated (hereinafter referred to collectively assubstrates) dip into the nontoxic electrolyte of the invention and formthe cathode. The electrolyte is preferably maintained in the range from20 to 70° C. It is possible to set a current density which is in therange from 0.01 to 100 ampere per square decimeter [A/dm²] and dependson the type of plating plant. In barrel plating plants, currentdensities in the range from 0.05 to 0.75 A/dm² are preferred, morepreferably from 0.1 to 0.5 A/dm² and very particularly preferably about0.3 A/dm². In rack plating processes, current densities in the rangefrom 0.2 to 10.0 A/dm² are preferably chosen, particularly preferablyfrom 0.2 to 5.0 A/dm² and very particularly preferably from 0.25 to 1.0A/dm².

Various anodes can be employed when using the nontoxic electrolyte ofthe invention. Soluble or insoluble anodes are suitable, as is thecombination of soluble and insoluble anodes.

As soluble anodes, preference is given to using anodes made of amaterial selected from the group consisting of electrolytic copper,phosphorus-containing copper, tin, tin-copper alloy, zinc-copper alloyand zinc-tin-copper alloy. Particular preference is given tocombinations of different soluble anodes made of these materials, andalso combinations of soluble tin anodes with insoluble anodes.

As insoluble anodes, preference is given to using anodes made of amaterial selected from the group consisting of platinized titanium,graphite, iridium-transition metal mixed oxide and special carbonmaterial (“Diamond Like Carbon”, DLC) or combinations of these anodes.Particular preference is given to mixed oxide anodes composed ofiridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide oriridum-tantalum mixed oxide.

If insoluble anodes are used, this is a particularly preferredembodiment of the process when the substrates to be provided withdecorative bronze layers, which represent the cathode, are separatedfrom the insoluble anode by an ion-exchange membrane so as to form acathode space and an anode space. In such a case, only the cathode spaceis filled with the nontoxic electrolyte of the invention. An aqueoussolution containing only a conductive salt is preferably present in theanode space. Such an arrangement prevents the anodic oxidation oftin(II) ions Sn²⁺ to tin(IV) ions Sn⁴⁺, which would have an adverseeffect on the plating process.

In membrane processes which are operated using insoluble anodes and thenontoxic electrolyte of the invention, current densities in the rangefrom 0.05 to 2 A/dm² are preferably set. The electrolyte is preferablymaintained in the range from 20 to 70° C. As ion-exchange membranes, itis possible to use cationic or anionic exchange membranes. Preference isgiven to using membranes composed of Nafion which have a thickness offrom 50 to 200 μm.

The disadvantage of additive-free phosphonate-based copper-tinelectrolytes is the restriction to a narrow current density range andthe lack of shine and the lower brightness of the layers deposited. Thenovel brightener system avoids these disadvantages in thephosphonate-based electrolyte system. Only when the electrolyte of theinvention is used is the deposition of bright and shiny layers madepossible over a wide current density range. None of the knowncyanide-free substitute processes (pyrophosphate, phosphonate,alkylsulfonate) achieves the properties of cyanide-containing baths(particularly in the case of shine and brightness, also only to anextent). The use of the brightener combination according to theinvention for the first time makes it possible to achieve the shine andbrightness which is comparable to the cyanide-containing electrolytes ofthe prior art and is thus significantly better than in all knowncyanide-free substitute processes.

In addition, management of the bath is simpler in the case of theelectrolyte of the invention. The novel brightener system enables theelectrolyte to be operated at higher copper contents. The combination ofthe compounds used, in particular those of the brightener systemcomprising carbonate ions and disulfide compounds, is critical here. Inthe presence of carbonate ions, even very small amounts of organicdisulfidates influence copper-tin alloy formation. In contrast toadditive-free baths, a largely constant alloy composition is obtainedover a wider current density range as a result of the addition of thebrightener system (FIG. 1—comparison of copper-tin electrolyte based onphosphonic acid with and without brightener system). In the case ofadditive-free baths, tin is deposited preferentially at higher currentdensities, which leads to a loss of shine of the layers.

For the purposes of the invention, (C₁-C₈)-alkyl is an alkyl radicalhaving from 1 to 8 carbon atoms. This can be branched as desired or inthe case of (C₃-C₆)-cycloalkyl be cyclic. This is, in particular,radicals such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl,isobutyl, pentyl, hexyl, cyclopropyl, cyclopentyl, cyclohexyl etc.

(C₈-C₁₈)-Arryl is an aromatic system which is made up entirely of from 6to 18 carbon atoms. This is, in particular, selected from the groupconsisting of phenyl, naphthyl, anthracenyl etc.

(C₇-C₁₉)-Alkylaryl radicals are radicals which have a (C₁-C₈)-alkylradical on the (C₆-C₁₈)-aryl radical.

(C₇-C₁₉)-Aralkyl radicals are radicals which have a (C₆-C₁₈)-arylradical on a (C₁-C₈)-alkyl radical, via which the radical is bound tothe molecule concerned.

According to the invention, a (C₃-C₁₈)-heteroaryl radical is an aromaticsystem which has at least three carbon atoms. In addition, furtherheteroatoms are present in the aromatic system. These are preferablynitrogen and/or sulfur. Such heteroaromatics are described, for example,in the book Bayer-Walter, Lehrbuch der Organischen Chemie, S. HirzelVerlag, 22nd edition, p. 703 ff.

For the purposes of the invention, (C₄-C₁₉)-alkylheteroaryl is a(C₃-C₁₈)-heteroaryl radical which is supplemented by a (C₁-C₈)-alkylsubstituent. The bonding to the molecule under consideration is via theheteroaromatic here.

Conversely, (C₄-C₁₉)-heteroaralkyl is a (C₃-C₁₈)-heteroaryl which isbound to the molecule concerned via a (C₁-C₈)-alkyl substituent.

For the purposes of the invention, halide encompasses chloride, bromideand fluoride.

The examples described below and the comparative example illustrate theinvention.

Alkyl(hetero)aryl is alkylaryl and alkylheteroaryl.

EXAMPLES

Comparison of brightness values for phosphonate electrolyte with andwithout brightener system (in L units according to the Cie-Lab method[http://www.cielab.de])

L*-values Current Current density density Current density 0.05 A/dm² 0.1A/dm² 0.2 A/dm² Phosphonate electrolyte 79.5 81.5 81.9 “withoutbrightener system” Phosphonate electrolyte 83.5 83.5 83.8 “withbrightener system”

The formation of dark streaks is significantly suppressed. Furthermore,the quality of the layer is maintained even in the case of thickdeposits.

An insoluble platinum-titanium anode was used in all experimentsdescribed.

Example 1 General Procedure

Barrel deposition of white bronze layers was carried out using anontoxic electrolyte according to the invention containing 100 g/l ofethylenediaminetetra(methylenephosphonic acid) EDTMP, 1.5 g/l of copperas copper hydroxide carbonate, 5 g/l of tin as tin pyrophosphate, 2 g/lof zinc as zinc pyrophosphate, 10 ml/l of methanesulfonic acid (70%), 20g/l of potassium hydrogencarbonate and 10 mg/l of bis(3-sodiumsulfopropyl) disulfide.

During the entire deposition procedure, the electrolyte was maintainedat 50° C. At a set current density of from 0.05 to 0.5 A/dm², opticallyuniform, high-shine bronze layers having the color typical of whitebronze were obtained in a drum plating apparatus.

Example 2 80 g/l of HEDP

50 ml/l of methanesulfonic acid (70%)10 g/l of potassium carbonate30 mg/l of 2,2′-dithiodipyridine1.47 g/l of copper pyrophosphate10.2 g/l of tin pyrophosphate2.5 g/l of zinc pyrophosphateParameters: pH 8.0/40° C./current densities: 0.05-0.5 A/dm²

Example 3 200 g/l of HEMPA

5 ml/l of propanesulfonic acid2 g/l of potassium hydrogencarboonate25 mg/l 2,2′-dithiodipyridine1.47 g/l of copper pyrophosphate10.2 g/l of tin pyrophosphate1.5 g/l of zinc pyrophosphate10 g/l citric acidParameters: pH 11.0/25° C./current densities: 0.05-0.5 A/dm²

Example 4 50 g/l of ATMP

100 g/l of potassium pyrophosphate20 g/l of citric acid4.2 g/l of copper hydroxide carbonate8.66 g/l of tin pyrophosphate4.5 g/l of zinc pyrophosphate10 g/l of potassium hydrogencarbonate0.5 g/l of 6,6′-dithiodinicotinic acidParameters: pH 9.0/60° C./current densities: 0.05-0.5 A/dm²

Example 5 Yellow Bronze 150 g/l of EDTMP

10 ml/l of methanesulfonic acid (70%)20 g/l of potassium carbonate9 g/l of copper hydroxide carbonate8.66 g/l of tin pyrophosphate5.5 g/l of zinc pyrophosphate15 mg/l of bis(3-sodium sulfopropyl) disulfideParameters: pH 10/60° C./current densities 0.05-0.5 A/dm²

1. A nontoxic electrolyte for the deposition of decorative bronze alloylayers on consumer goods and industrial articles, which contains themetals to be deposited in the form of water-soluble salts, wherein theelectrolyte comprises one or more phosphonic acid derivatives ascomplexing agents and a brightener system composed of a disulfidecompound and a carbonate or hydrogencarbonate salt.
 2. The electrolyteas claimed in claim 1, wherein, it contains the metal ions of copper andtin or copper, tin and zinc to be deposited.
 3. The electrolyte asclaimed in claim 2, wherein the water-soluble salts of the metals to bedeposited are selected from the group consisting of pyrophosphates,carbonates, hydroxide-carbonates, hydrogencarbonates, sulfites,sulfates, phosphates, nitrites, nitrates, halides, hydroxides,oxide-hydroxides, oxides and combinations thereof.
 4. The electrolyte asclaimed in claim 1, wherein the metals to be deposited are present indissolved form, with the ion concentration of copper being in the rangefrom 0.2 to 10 gram per liter of electrolyte, the ion concentration oftin being in the range from 1.0 to 30 gram per liter of electrolyte andthe ion concentration of zinc, if present, being in the range from 1.0to 20 gram per liter of electrolyte.
 5. The electrolyte as claimed inclaim 1, wherein it comprises, as carbonate or hydrogencarbonate salt, asalt of this type selected from the group consisting of alkali metal andalkaline earth metal salts.
 6. The electrolyte as claimed in claim 5,wherein the carbonate or hydrogencarbonate ions are present in an amountof 0.5-100 g/l of electrolyte.
 7. The electrolyte as claimed in claim 1,wherein it comprises, as disulfide compound, a compound of this typeselected from the group consisting of substituted and unsubstitutedbisalkyl or bis(hetero)aryl or alkyl (hetero)aryl disulfides.
 8. Theelectrolyte as claimed in claim 7, wherein the disulfide compound ispresent in the electrolyte in an amount of 0.01 mg/l-10.0 g/l.
 9. Theelectrolyte as claimed in claim 1, wherein it contains, as phosphonicacid derivatives, one or more compounds selected from the groupconsisting of 1-aminomethylphosphonic acid AMP,aminotris(methylenephosphonic acid) ATMP, 1-aminoethylphosphonic acidAEP, 1-aminopropylphosphonic acid APP,(1-acetylamino-2,2,2-trichloroethyl)phosphonic acid,(1-amino-1-phosphonooctyl)phosphonic acid,(1-benzoylamino-2,2,2-trichloroethyl)phosphonic acid,(1-benzoylamino-2,2-dichlorovinyl)phosphonic acid,(4-chlorophenylhydroxymethyl)phosphonic acid,diethylenetriamine-penta(methylenephosphonic acid) DTPMP,ethylenediaminetetra(methylenephosphonic acid) EDTMP,1-hydroxyethane(1,1-di-phosphonic acid) HEDP,hydroxyethylaminodi(methylenephosphonic acid) HEMPA,hexamethylenediaminetetra(methylphosphonic acid) HDTMP,((hydroxymethylphosphonomethylamino)methyl)phosphonic acid,nitrilotris(methylenephosphonic acid) NTMP,2,2,2-trichloro-1-(furan-2-carbonyl)amino-ethylphosphonic acid, saltsderived therefrom and condensates derived therefrom, or combinationsthereof.
 10. The electrolyte as claimed in claim 1, wherein the pH ofthe electrolyte is in the range from 6 to
 14. 11. The electrolyte asclaimed in claim 1, wherein pyrophosphate ions are present in theelectrolyte.
 12. The electrolyte as claimed in claim 1, wherein one ormore stabilizing compounds selected from the group consisting ofmonocarboxylic and dicarboxylic acids, alkanesulfonic acids, betainesand aromatic nitro compounds are present.
 13. A process for theelectrochemical application of decorative bronze alloy layers toconsumer goods and industrial articles, in which the substrates to becoated are dipped into an electrolyte containing the metals to bedeposited in the form of water-soluble salts, wherein a nontoxicelectrolyte as claimed in claim 1 is used.
 14. The process as claimed inclaim 13, wherein the electrolyte is maintained in the range from 20 to70° C. during deposition of the metals.
 15. The process as claimed inclaim 13, wherein a current density in the range from 0.01 to 100 ampereper square decimeter is set.